A crucible formed from a high melting point metal is used to melt lumps of rare earth metallic raw material so as to cast them into ingots, or to melt and refine rare earth oxide raw materials using the heat reduction of calcium. These processes are performed in a vacuum melting furnace. Specifically, these processes are performed by first placing a crucible containing the raw materials in a vacuum furnace. Air is then expelled from the vacuum furnace and the vacuum furnace is refilled with an inert gas (i.e., argon or the like). Induction heating is used for the melting (see, for example, Patent document 1).
In an induction heating type of melting furnace of a related art, once a melting furnace melts a material, it is necessary for the crucible to be cleaned. However, because the temperature inside a crucible after the melting and heating is extremely high, maintenance work cannot begin until the temperature cools enough to allow maintenance work to be carried out. This places severe restrictions on the work cycle.
Previously, the cooling of a crucible after melting and heating has relied on heat conduction generated by the flow of cooling water inside a coil that is used for the induction heating, or on radiation from the surface of the crucible. Because the cooling obtained from heat conduction occurs via an insulating material, it is extremely weak and, in actuality, almost all of the cooling is achieved through radiation. In cooling achieved through radiation in this manner, considerable time is required until the crucible cools sufficiently and this thwarts any attempt to improve the work cycle.